UV RADIATION MUTAGENESIS: We plan to characterize the multiple, independent processes for UV radiation mutagenesis in E. coli K-12 uvrB5 (i.e., the one-hit, and "?-hit" process). (1) Do they produce different classes of mutations (i.e., back, suppressor, etc.)? (2) Do they work on different kinds of mutagenic lesions (i.e., dimer, nondimer, etc.)? (3) Are they controlled by different DNA repair genes? (4) Is one-hit UV radiation mutagenesis constitutive? (5) Why are the growth-dependent kinetics of missense and nonsense reversion different? (6) Why are Lac+ back mutants produced with one-hit kinetics while Leu+ (missense) revertants are produced with both one-hit and two-hit kinetics? (7) What is the effect of the DNA base sequence on mutagenesis at a particular site? SPONTANEOUS MUTAGENESIS: We have observed that mutations in genes that control DNA repair and increase (or decrease) UV radiation mutagenesis, also increase (or decrease) spontaneous mutagenesis. We wish to determine the source and nature of the spontaneous, excisable lesions in DNA that produce spontaneous mutations. POSTREPLICATION REPAIR (PRR): Projects: (1) What additional genes are involved in PRR, and do they function in the recF-dependent pathway or in the recB, uvrD, lexA-dependent pathway, or are they required in both pathways of PRR? [Note: We will concentrate initially on the lexC, umuC, dam, and radA genes.] (2) Does a recF mutation completely block PRR in a uvrB strain at UV radiation fluences above 1 J m-2? (3) What is the molecular basis of the UV radition-induced resistance to UV radiation in a urvB strain? (4) Is the recF gene product an endonuclease that is specific for single-stranded DNA? (5) Do the recB, uvrD, and lexA gene products (or gene products regulated by lexA) function in PRR as part of a protein complex? HEALTH RELATEDNESS: Since UV radiation mutagenesis is due to errorprone DNA repair, and since almost all ultimate carcinogens are mutagens, it implies that an error in DNA repair may be one of the first molecular events that leads to carcinogenesis. Thus, through a better understanding of the molecular mechanisms for DNA repair and mutagenesis should come a better understanding of the molecular basis of carcinogenesis.